The purpose of this proposal is to apply the noninvasive method of computerized tomographic scanning to the quantitative measurement of vertebral body changes that are occurring in a well established dog model of age-related osteopenia, and to establish the vertebral body changes in this model. We intend to determine if a long-term weightlifting exercise program has enhanced bone mineral in a group of six year old Beagles who are on the verge of entering the time frame when age-related osteopenia develops. We plan to sequentially scan each dog for the next three years and determine if weightlifting exercise will prevent or retard the osteopenic phenomenon. To acccomplish this objective, we intend to use computerized tomography in scanning for bone density changes in the second lumbar vertebra of both weightlifting and control Beagles. These measurements will also be correlated with tibial mineral measurements acquired through the use of I-125 photon absorptiometry. By determining if bone loss can be prevented in both the vertebra and tibia through weightlifting exercise, we can determine whether this form of therapy has clinical application in preventing the development of osteoporosis in humans. We will also be able to determine whether or not there is a different skeletal response to exercise in the axial versus appendicular skeleton.